1. Field
This document relates to a stereoscopic image display.
2. Related Art
Glass type stereoscopic image displays are divided into a polarization glasses type and a shutter glasses type. The polarization glasses type requires a polarization separation device, such as a patterned retarder, to be bonded to a display panel. The patterned retarder separates the polarizations of a left-eye image and a right-eye image displayed on the display panel. A viewer wears polarization glasses when viewing a stereoscopic image on the polarization glasses type stereoscopic image display to see the polarization of the left-eye image through a left-eye filter of the polarization glasses and the polarization of the right-eye image through a right-eye filter of the polarization glasses, thereby giving a stereoscopic feeling.
The display panel of the conventional polarization glasses type stereoscopic image display may be a liquid crystal display panel. A parallax is generated between a pixel array of the liquid crystal display panel and the patterned retarder due to the thickness of an upper glass substrate of the liquid crystal display panel and the thickness of an upper polarization substrate, and this leads to a poor vertical viewing angle. When the viewer views a stereoscopic image displayed on the polarization glasses type stereoscopic image display at a vertical viewing angle higher or lower than the front surface of the liquid crystal display panel, they may feel a 3D crosstalk where the left eye image and the right eye image overlap each other when viewing them with a single eye (left eye or right eye).
In order to solve the problem of 3D crosstalk at vertical viewing angle in the polarization glasses type stereoscopic image display, Japanese Laid Open Publication NO. 2002-185983 proposed a method for forming black stripes on a patterned retarder (or 3D film) of a stereoscopic image display. In a method different from this method, the width of black matrices formed on a liquid crystal display panel can be increased. However, the formation of black stripes on the patterned retarder may result in a reduction in luminance of 2D/3D images, and the black matrices may interact with the black stripes, thereby generating moiré. Also, an increase in the width of black matrices may reduce aperture ratio, thereby degrading luminance of 2D/3D images.
The present applicant proposed the technique of dividing each of pixels of a display panel into two parts and using one of the two parts by an active black stripe in U.S. patent application Ser. No. 12/536,031 (Aug. 5, 2009). The stereoscopic image display proposed by the present applicant can provide more excellent display quality than the existing stereoscopic image display, by offering the advantages of preventing a reduction in luminance of a 2D image by dividing each of the pixels into the two parts and writing 2D image data to each of the divided pixels in a 2D mode, and improving the visibility of both the 2D and 3D images by widening a vertical viewing angle in a 3D image. The active black stripe may include a thin film transistor (hereinafter, “TFT”) and a liquid crystal cell.
The active black stripe technology proposed by the present applicant requires discharging of the voltage of a liquid crystal cell to a black gray voltage. To this end, a relatively high voltage may be applied to a gate of the TFT included in the active black stripe so that on current flows in the TFT during a predetermined period of time. In this case, the TFT of the active black stripe may undergo degradation in driving characteristics, including a threshold voltage shift caused by a gate bias stress. To increase the completeness of the active black stripe technology in the 3D mode, it is necessary to guarantee enough discharging time of active black stripes across the entire screen so that the active black stripes on the entire screen can represent a black gray scale.